Naphthalene-based turn-on fluorescent probe for sensitively recognizing Zn²⁺

A Schiff-base type fluorescent sensor (PLB3) was synthesized by nucleophilic addition-elimination between 2-hydroxy-1-naphthaldehyde and 5-chloro-2-aminopyridine. Single crystal X-ray diffraction analysis demonstrated keto-amine isomer was predominantly adopted. 8-Fold fluorescence-enhanced recognition for detecting Zn2+ was chelation enhanced fluoresce (CHEF) mechanism. Also, PLB3 could distinguish well Zn2+ from analogue Cd2+. Job's plot fluorescence titration and UV-Vis titration revealed the 1:1 stoichiometry between Zn2+ and PLB3. The association constant (K-a) and limit of detection (LOD) were 5.14 x 10(7) M-1 and 0.33 mu M, respectively. The excellent selective and sensitive properties urge PLB3 to detect the trace amounts of Zn2+ in the environmental systems.